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Biofouling is one of the major factors causing decline in membrane performance in reverse osmosis (RO) plants, and perhaps the biggest hurdle of membrane technology. Chemical cleaning is periodically carried out at RO membrane installations aiming to restore membrane performance. Typical cleaning agents used in the water treatment industry include sodium hydroxide (NaOH) and hydrochloric acid (HCl) in sequence. Rapid biofilm regrowth and related membrane performance decline after conventional chemical cleaning is a routinely observed phenomenon due to the inefficient removal of biomass from membrane modules. Since extracellular polymeric substances (EPS) make up the strongest and predominant structural framework of biofilms, disintegration of the EPS matrix should be the main target for enhanced biomass removal. Previously, we demonstrated at lab-scale the use of concentrated urea as a chemical cleaning agent for RO membrane systems. The protein denaturation property of urea was exploited to solubilize the proteinaceous foulants, weakening the EPS layer, resulting in enhanced biomass solubilization and removal from RO membrane systems. In this work, we investigated the impact of repeated chemical cleaning cycles with urea/HCl as well as NaOH/HCl on biomass removal and the potential adaptation of the biofilm microbial community. Chemical cleaning with urea/HCl was consistently more effective than NaOH/HCl cleaning over 6 cleaning and regrowth cycles. At the end of the 6 cleaning cycles, the percent reduction was 35% and 41% in feed channel pressure drop, 50% and 70% in total organic carbon, 30% and 40% in EPS proteins, and 40% and 66% in the peak intensities of protein-like matter, after NaOH/HCl cleaning and Urea/HCl cleaning, respectively. 16S ribosomal RNA (rRNA) gene sequencing of the biofilm microbial community revealed that urea cleaning does not select for key biofouling families such as Sphingomonadaceae and Xanthomonadaceae that are known to survive conventional chemical cleaning and produce adhesive EPS. This study reaffirmed that urea possesses all the desirable properties of a chemical cleaning agent, i.e., it dissolves the existing fouling layer, delays fresh fouling accumulation by inhibiting the production of a more viscous EPS, does not cause damage to the membranes, is chemically stable, and environmentally friendly as it can be recycled for cleaning.

Chemical cleaning is routinely performed in reverse osmosis (RO) plants for the regeneration of RO membranes that suffer from biofouling problems. The potential of urea as a chaotropic agent to enhance the solubilization of biofilm proteins has been reported briefly in the literature. In this paper the efficiency of urea cleaning for RO membrane systems has been compared to conventionally applied acid/alkali treatment. Preliminary assessment confirmed that urea did not damage the RO polyamide membranes and that the membrane cleaning efficiency increased with increasing concentrations of urea and temperature. Accelerated biofilm formation was carried out in membrane fouling simulators which were subsequently cleaned with (i) 0.01M sodium hydroxide (NaOH) and 0.1M hydrochloric acid (HCl) (typically applied in industry), (ii) urea (CO(NH2)2) and hydrochloric acid, or (iii) urea only (1340 g/Lwater). The pressure drop over the flow channel was used to evaluate the efficiency of the applied chemical cleanings. Biomass removal was evaluated by measuring chemical oxygen demand (COD), adenosine triphosphate (ATP), protein, and carbohydrate content from the membrane and spacer surfaces after cleaning. In addition to protein and carbohydrate quantification of the extracellular polymeric substances (EPS), fluorescence excitation−emission matrix (FEEM) spectroscopy was used to distinguish the difference in organic matter of the remaining biomass to assess biofilm solubilization efficacy of the different cleaning agents. Results indicated that two-stage CO(NH2)2/HCl cleaning was as effective as cleaning with NaOH/HCl in terms of restoring the feed channel pressure drop (>70% pressure drop decrease). One-stage cleaning with urea only was not as effective indicating the importance of the second-stage low pH acid cleaning in weakening the biofilm matrix. All three chemical cleaning protocols were equally effective in reducing the concentration of predominant EPS components protein and carbohydrate (>50% reduction in concentrations). However, urea-based cleaning strategies were more effective in solubilizing protein-like matter and tyrosine-containing proteins. Furthermore, ATP measurements showed that biomass inactivation was up to two-fold greater after treatment with urea-based chemical cleanings compared to the conventional acid/alkali treatment. The applicability of urea as an alternative, economical, eco-friendly and effective chemical cleaning agent for the control of biological fouling was successfully demonstrated. Keywords: Reverse osmosis, Biofouling, Membrane fouling simulator, Chemical cleaning, Urea

The present work explores a controversy surrounding gender equity in surgical residency programs, particularly focusing on the Stanford University and University of Washington (UW) General Surgery Residency cohorts. While the Stanford cohort, which consisted mostly of women, faced criticism from nonmedical audiences claiming that gender was prioritized over qualifications, the all-male radiology residents received less attention and fewer criticisms. The article highlights the double standards and challenges the notion of meritocracy. It discusses the gender and racial disparities in surgical residency programs, emphasizing the need for diversity and inclusion. The presence of diverse female representation is seen as a valuable asset that brings compassion, teamwork, and inclusive leadership to the field. The article calls for active support from institutions, male allies, and transparency in collecting applicant demographic data to address biases and promote gender diversity in surgery., (Copyright © 2023 Association of Program Directors in Surgery. Published by Elsevier Inc. All rights reserved.)

Toxic metal pollutants threaten water environment. It exists undesirably metal-ion concentration limits with conventional precipitation flotation. An enhanced precipitation flotation system focusing on efficient removal for bivalent metal-ions was researched. The system involved the addition of humics and Fe 3+ to generate and regulate the precipitates. The characteristics of precipitates were investigated by particle analysis, conditional stability constants and DLVO theory calculations, and SEM&TEM imaging. The results reveal that metal-ions chelate with humics at low metal-ion concentration, with generating the limited micro-size precipitates of <2.0 μm, fractal dimension of 1.60-1.80 and precipitate efficiency of <91.00%. By adding trivalent Fe 3+ , the macro-size precipitates are obtained with particle size of approximate 10.0 μm, fractal dimension of 1.50-1.60, and nearly-total flotation removal of precipitate. The chelating interaction of Fe 3+ with humics is the mainly regulating mechanism, which could enhance the conditional stability constants and the precipitate efficiency of metal-ions at low concentration. The desired precipitate particles are finally obtained by breaking the limitations of metal-ion concentration. Finally, the flotation removal of metal-ions from single or mixed solutions is respectively 99.10 ± 0.10% for Cu 2+ , 99.60 ± 0.10% for Pb 2+ , and 94.30 ± 0.30% for Zn 2+ . Therefore, the enhanced precipitation flotation process is an efficient purification approach for metal-containing wastewaters., (Copyright © 2019 Elsevier B.V. All rights reserved.)